Conventionally, an armature core of a motor has been press fitted to an armature shaft by means of a presser having a hydraulic cylinder.
In the case where a portion that is pushed out and projecting from the armature core (i.e. an one end of the armature shaft in the press fitting direction) is required to have a specific length, a stopper should be provided at a position within a prespecified distance from the touching surface between the armature core and a jig holding the armature. Therefore, the end of the projecting armature shaft is stopped by the stopper so that the relative position of the armature core and the armature shaft can be set at the desired distance. The above method is called a constant size press fitting method.
However, in the above method, it is difficult to exchange the stopper when various relative positions are required for a plurality of armature cores and armature shafts, and when various types of products are to be manufactured. Furthermore, when the stopper is worn, the press fitted length of the armature shaft with respect to the armature core will become variable so that the entire armature assembly will be variable and consequently the reliability of the product will not be maintained. In addition, when the armature shaft is pushed out by the presser and collides with the worn stopper, the armature shaft will be chewed by the presser and the stopper, and the hydraulic pressure of the driving cylinder that is applied. Therefore, the thin shaft of the press fitting body may be bent during this process.